Acta Societatis pro Fauna et Flora Fennica, 49, N:o 7. 25 



late 2 — 4-dentatis; tumoribus basalibus nullis. Long'. 228 

 274—277, lat. 213—236-247, isthm. 34, long. pol. lob. 

 64—72. — PI. 1 fig. 15. 



Finally I have seen a form which might be f. evoluta 

 Turn., but the spines of the ultimate lobules are, very 

 characteristically, quite tangentially directed. Long. 281, lat. 

 251 //. — PI. 1 fig. 17—18. 



M. denticulata Breb. and some allied species. 



This species and its nearest relatives viz. M. thomasiana 

 A r c h., M. angulosa Hantzsch, M. verrucosa B i s s., have 

 been identified in quite different ways by different authors. 

 The reason for this is that the figures published commonly 

 were very inaccurate, but also that the number of the various 

 forms is very considerable. If I shall not be able now fully to 

 clear up this question, I think these remarks might be of 

 some value in stimulating other algologists to further study 

 of these forms. 



The typical M. denticulata l ) has all lobules with rounded 

 angles, not acute or spinate. (Ralfs, Br. D. p. 70 pi. 7 

 f. 1; De Toni, Sylloge I p. 1130; West, Mngr. II p. 105 

 pi. 49 f. 1—6 and pi. 50 f. 1—2). Across the base of the 

 semicells are three flattened rounded protuberances. Such 

 a form at first very much resembles M. angulosa 2 ) (in 

 West: M. denticulata var. angulosa) from which it is easily 

 distinguished by its longer (commonly more than 70/0 polar 

 lobe with its concave sides, whereas M. angulosa always 

 has a very short polar lobe (from 42 to 62, a at most). The 

 best differential character is seen in the vertical view: 

 M. denticulata with strongly undulated margins (correspond- 

 ing to the basal protuberances in front view), whereas 

 M. angulosa in vertical view is not undulated but at the 

 middle very thick, so that it becomes the shape of a 

 flattened rhomboid. M. angulosa is a well characterized 

 species and should not be confused with M. denticulata. 



\) Vide PI. 2 fig. 6 7. 

 -i Vide pi. 2 fig. 4—5. 



